Kailua-Kona town, Kahaluʻu’s bacteria problem, Magic Sands, and the Keauhou area.
The Hawaii Department of Health recommends staying out of the ocean for at least 72 hours after heavy rain. Kona’s coast is dry, but Kahaluʻu Bay has chronic bacteria contamination from freshwater springs carrying cesspool waste through porous lava rock. The 72-hour rain rule is especially important here.
The Kona Coast is the Big Island’s main tourist hub, centered around the town of Kailua-Kona on the dry western shore. Unlike the luxury resort corridor of the Kohala Coast to the north, Kona is a working town with restaurants, shops, grocery stores, and a walkable waterfront. Aliʻi Drive, the main coastal road, runs about 6 miles south from the town center to the Keauhou area.
Visitors come for the water activities — snorkeling at Kahaluʻu, manta ray night dives from Keauhou Bay, deep-sea fishing from Honokohau Harbor, and scuba diving along the coast’s clear waters. The town also hosts the annual Ironman World Championship triathlon.
The coastline is mostly rocky lava rather than continuous sand beach. The dry climate (about 20 inches of rain per year) would suggest clean water, but Kona has a unique challenge: submarine groundwater discharge carrying cesspool contamination through porous basalt lava rock, particularly severe at Kahaluʻu Bay.
Kahaluʻu Beach Park — Kona’s most popular snorkeling spot. Has a chronic bacteria problem (92% test failure rate) from cesspool-contaminated groundwater springs.
Magic Sands (Laʻaloa Beach Park) — Small beach where the sand disappears during high surf. Bodyboarding, lifeguard. Better water quality than Kahaluʻu.
Two Step (Honaunau Bay) — About 20 minutes south of Kona town. Excellent snorkeling with cleaner water than Kahaluʻu.
Kailua-Kona is the main tourist town on the Big Island’s dry western coast. Aliʻi Drive runs along the waterfront for about 6 miles from the town center south to Keauhou. Unlike Waikiki’s continuous sand beach, Kona’s coast is mostly rocky lava shoreline with small beach pockets.
Important: "Kailua-Kona" is NOT the same as "Kailua" on Oʻahu. They are on different islands. Read our disambiguation guide →
Kahaluʻu is Kona’s most popular snorkeling beach. Shallow reef, abundant sea turtles, easy entry. But it has a 92% bacteria test failure rate — one of the worst in Hawaiʻi. Freshwater springs discharge cesspool-contaminated water through the lava rock into the bay. This is a chronic, geological condition, not weather-dependent. If you snorkel here, avoid swallowing water, cover any open cuts, and shower with soap immediately after.
Known as "Magic Sands" because the sand disappears during high surf, exposing the rocky bottom, then returns when waves calm. Small beach with bodyboarding and bodysurfing. Water quality is generally better than Kahaluʻu because it has more open-ocean exposure and flushing. Lifeguard on duty.
Hotels: Sheraton Kona Resort & Spa, Outrigger Kona Resort
Keauhou Bay is primarily a boat harbor for manta ray night snorkel/dive tours. The Sheraton has a manta ray viewing area where mantas come nightly to feed on plankton attracted by spotlights. Limited beach swimming in this area — it’s more about boat-based activities.
Kona’s coast is generally dry, but the water quality picture is complicated by submarine groundwater discharge. Cold freshwater flows through the porous basalt lava from the slopes of Hualalai and Mauna Loa, carrying bacteria from the estimated 50,000+ cesspools in West Hawaiʻi. This freshwater emerges as springs along the coast, particularly at Kahaluʻu. Beaches with more open-ocean exposure (like Magic Sands) flush better than enclosed bays (like Kahaluʻu).
Sheraton Kona Resort & Spa at Keauhou Bay — South of town on lava cliffs. Famous manta ray viewing from the waterfront.
Outrigger Kona Resort & Spa — Near Keauhou. Condo-style property with kitchens. Good for families.
From Kona Airport (KOA): Kailua-Kona town is about 7 miles south, a 15-20 minute drive. Keauhou is another 10 minutes south.
Parking: Limited street parking along Aliʻi Drive. Public lot near Kailua Pier (metered). Kahaluʻu and Magic Sands have small lots that fill early on weekends. A rental car is essential.
Restrooms: Kahaluʻu has full facilities including lifeguard station. Magic Sands has restrooms and lifeguard. Kailua Pier area has public restrooms.
Kona’s west-facing coast is a year-round destination. Summer months (May-September) have the calmest seas and best visibility for snorkeling and diving. The groundwater-driven bacteria contamination at Kahaluʻu is chronic and not seasonal. Manta ray viewing at Keauhou Bay is available nightly throughout the year.
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Every beach page on this site includes a historical bacteria risk rating from 1 (low) to 5 (high), based on DOH testing data, Surfrider Foundation monitoring, geographic factors like stream proximity and cesspool contamination areas, and historical advisory frequency. These ratings reflect long-term patterns — not current conditions. Always check the live advisory status at the top of each beach page before swimming.
The Hawaii Department of Health monitors approximately 57 beaches statewide through its Tier 1 and Tier 2 testing programs. Many popular beaches have no regular testing. This site aggregates data from DOH, USGS stream monitoring, NOAA ocean conditions, and NWS weather alerts to provide broader coverage.
After heavy rain, streams carry bacteria, sewage, pesticides, and sediment into the ocean. Bacteria levels can be dangerously high even when the water appears clear. The DOH recommends waiting at least 72 hours after heavy rain before swimming, especially near stream mouths and canal outlets.
Beaches on dry, leeward coasts typically recover faster than beaches near major stream outlets. Open ocean beaches with strong wave action flush contamination more quickly than sheltered bays and lagoons.
100+ beaches across all islands
Safe to Swim Hawaii aggregates water quality data from six independent sources to provide broader coverage than any single agency. Our sources include the Hawaii Department of Health Clean Water Branch (beach advisories and bacteria testing), USGS National Water Information System (25 stream monitoring stations across all islands), NOAA CO-OPS (tide levels and water temperature), NDBC (wave buoys and ocean conditions), NWS Honolulu (weather and marine alerts), and City & County of Honolulu Environmental Services (Kailua Bay water testing and spill reports).
Historical bacteria risk ratings on this site are based on DOH testing data, Surfrider Foundation monitoring, geographic analysis (stream proximity, cesspool contamination areas, coastal development), and advisory frequency. These are historical assessments, not live measurements. Always check the live advisory status at the top of each page and verify conditions with the Hawaii DOH Clean Water Branch before entering the water.
Less rainfall means less runoff and generally cleaner ocean water across all islands. Stream flows drop, reducing bacteria transport to coastal areas. This is typically the best time for ocean water quality, though localized contamination from cesspools and urban runoff can still occur.
Frequent heavy rain events cause stream flooding, sewage overflows, and brown water advisories. Windward and north-facing coasts receive more rain. The DOH issues the most advisories during this period. Leeward coasts (west-facing) generally stay drier and cleaner year-round.
Water quality patterns vary significantly by location. Beaches near stream mouths and urban areas show the most dramatic seasonal variation. Open ocean beaches with strong wave action maintain better water quality year-round. Check individual beach pages for location-specific seasonal data.
Hawaii has approximately 88,000 cesspools — more than any other U.S. state. These underground chambers collect untreated household sewage and allow it to leach into the surrounding soil and groundwater. In coastal areas, this contaminated groundwater eventually reaches the ocean through submarine groundwater discharge, contributing to elevated bacteria levels at nearby beaches.
Hawaii Act 125 (2017) requires all cesspools to be upgraded or converted to approved septic systems by 2050. Priority areas near the coast and drinking water sources are being addressed first, but progress has been slow. Beaches in known cesspool contamination zones carry elevated bacteria risk even during dry weather. For more information, see our comprehensive cesspool guide.
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings are estimates based on publicly available testing data and geographic analysis. They are not real-time measurements and may not reflect current conditions.
Always verify current water quality conditions with the Hawaii DOH Clean Water Branch before entering the water.
This site does not recommend or advise anyone to swim at any beach. We share government data and geographic analysis so you can make your own informed decisions. By using this site you accept full responsibility for your own safety. See our Terms of Use for full details.
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Safe to Swim Hawaii checks water quality data every 15 minutes from multiple government agencies. When conditions change — a new advisory is posted, stream levels spike after rain, or an advisory is cancelled — our pages update automatically. This means you are seeing the latest available data from official sources, not a static snapshot.
The Hawaii Department of Health Clean Water Branch operates the state’s official beach monitoring program. Tier 1 beaches are tested weekly; Tier 2 beaches are tested less frequently. When bacteria levels exceed 130 enterococci per 100 mL, the DOH issues a Beach Advisory for that location. Brown Water Advisories are issued based on visual assessment of runoff conditions, not bacteria testing.
USGS stream monitoring stations measure water flow (discharge) and turbidity in real time. When a stream near a beach is flowing at 5x or more above its normal rate, this indicates significant runoff that likely carries elevated bacteria. We display these stream conditions alongside DOH advisories to give a more complete picture of water quality at each beach.